Phenol and cyclohexanone are important materials in the chemical industry and are useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, a common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of cumene to the corresponding hydroperoxide, and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene feed is generally high.
Thus, a process that uses higher alkenes instead of propylene as feed and coproduces higher ketones, such as cyclohexanone, rather than acetone may be an attractive alternative route to the production of phenols. There is also a growing demand for cyclohexanone.
It is known from, e.g., U.S. Pat. No. 6,037,513 that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a bifunctional catalyst comprising a molecular sieve of the MCM-22 type and at least one hydrogenation metal selected from Pd, Ru, Ni, Co, and mixtures thereof. This reference also discloses that the resultant cyclohexylbenzene can be oxidized to the corresponding hydroperoxide which is then decomposed to the desired phenol and cyclohexanone co-product.
It has been found that in hydroalkylation process of an aromatic compound such as benzene, a non-negligible amount of olefins, especially phenylcyclohexene, is produced. Phenylcyclohexene is difficult to separate from cyclohexylbenzene due to their close boiling. If left unconverted to cyclohexylbenzene, phenylcyclohexene will be eventually converted into undesirable by-products, which will be discarded and cause a yield loss. Thus, WO 2011/100013 A1 teaches combining the phenylcyclohexene-containing hydroalkylation stream with other phenylcyclohexene-containing recycle stream(s), and subjecting the combined stream to hydrogenation to convert phenylcyclohexene into cyclohexylbenzene. This process would require a dedicated, separate and stand-alone hydrogenation reactor for this purpose.
Therefore, there is a need for an improved hydroalkylation process.